Hidden treasures in archived invertebrate collections: Exploring past resource use from preserved gut contents

The River Continuum Concept (RCC) was an influential concept that described the physical, biological, and chemical changes occurring along a longitudinal gradient in stream networks.  Aquatic insect specimens (collected on the Salmon River, Idaho in 1976) that were a significant component of the RCC studies were preserved, archived, and left untouched for 33 years.  As part of a larger project, we performed gut content analysis on these archived specimens.  Specimens were originally preserved in formalin and transferred to ethanol for long-term storage. The condition of the archived samples was variable; some vials lacked ethanol and insects were desiccated.  Despite 30 years of storage and variable preservation, the gut content was remarkably intact and diatoms could be identified to the species level. Desiccated specimens were successfully revived by adding ethanol.  We found that the proportion of leaves in invertebrate diets was higher in the headwaters and the proportion of diatoms was highest in the mid-reaches further confirming the predictions of the RCC.  Gut contents of archived specimens may be a promising tool to examine the effects of changes on stream ecosystems such as global change, species invasions, extirpations and land conversion.